The present invention relates to a method of insulating a well bore with an oil base packer fluid.
Permafrost is a thick layer of frozen surface ground which may be several hundred feet thick. Commonly, in recovering oil and gas through permafrost zones, several concentric casing strings are set through the permafrost. Water and water based muds used in the drilling operation tend to accumulate between the casing strings and are subjected to freezing temperatures for extended periods of time after the wells are drilled. When this occurs, casing collapse or rupture can result from the severe stresses imposed by the volume increase of the freezing water. Additionally, since oil and gas produced is generally at elevated temperatures, e.g., greater than 150.degree. F., considerable thawing and softening of the normally hard permafrost around the borehold occurs. This leads to subsidence of the earth and damage to the casing and tubing.
U.S. Pat. No. 3,831,678, incorporated herein by reference, contains a discussion of prior art techniques which have been tried in an attempt to solve the problems discussed above with regard to the production of oil and gas through permafrost. Additionally, U.S. Pat. No. 3,650,327 discloses a method for effecting thermal insulation of wells such as, for example, a well through a permafrost zone.
In the method described and claimed in U.S. Pat. No. 3,831,678, an oil based packer fluid is utilized, the packer fluid containing an organic modified clay which is a gellant for oleaginous mediums. The gellants employed do not function effectively at temperatures less than about 50.degree. F. However, upon raising the temperature of the well packer fluid above about 50.degree. F., gelation occurs, the degree of which depends upon the composition of the packer fluid and the temperature to which it is subjected. The method disclosed in U.S. Pat. No. 3,831,678 is inherently limited to use in at temperatures below about 50.degree. F. since at higher temperatures the packer fluid thickens and can accordingly, not be pumped into an annulus of a well bore to serve as an insulating medium.